The present inventor is also the inventor of the sound absorbing structures set forth in U.S. Pats. Nos. 4,141,433; 4,243,117; and 4,339,018, incorporated herein by reference, which relate to the absorption of sound utilizing compact lightweight structures typical of those used in aerospace construction. In such structures, a plurality of specifically deployed adjacent cavities serve to act as an array of sound absorbing members.
In addition to the above referenced patents, the present inventor is also the inventor of co-pending patent application Ser. No. 09/320,415 entitled, xe2x80x9cStructure for Absorbing Sound.xe2x80x9d The structures described in this co-pending application make use of any material as a sound absorber, not depending on or requiring the use of materials such as open cell plastic foam or fibrous materials that have inherently high sound absorption. The structures described in this co-pending application employ the quarter-wave resonator principle.
It is an object of the present invention to create an absorber that has a very wide frequency range of absorption which would have a wide variety of specialized applications including ceiling and wall treatments, machinery enclosures, and office partitions using the advantages of interference between closely spaced quarter wave resonators and/or Helmholtz resonators.
These and other objects have been accomplished by novel sound absorption structures that are essentially flat and very compact.
New sound absorbing structures that are very flat and compact have been discovered. The sound absorbing qualities of such structures are dependent on the structure=s geometry and not the material of construction. The structures do not depend on or require the use of materials such as open cell plastic foam or fibrous materials that have inherently high sound absorption. These structures use the advantages of interference between closely spaced quarter wave resonators and/or Helmholtz resonators.
This invention may take many forms. It is basically a multi-ply sandwich construction consisting of a front and rear face of sound reflecting material and an inner core made up of walls defining a series of quarter wave resonators and/or Helmholtz resonators with a continuous progression of resonant frequencies from the lowest desired frequency for sound absorption to the highest desired frequency for sound absorption.